Date:   Fri, 26 Nov 2021 02:33:51 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Adam Ford <aford173@...il.com>
Cc:     Jagan Teki <jagan@...rulasolutions.com>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Tim Harvey <tharvey@...eworks.com>,
        Schrempf Frieder <frieder.schrempf@...tron.de>,
        linux-media <linux-media@...r.kernel.org>,
        Adam Ford-BE <aford@...conembedded.com>,
        cstevens@...conembedded.com, Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Peng Fan <peng.fan@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/5] soc: imx: imx8m-blk-ctrl: Fix imx8mm mipi reset

Hi Adam,

On Thu, Nov 25, 2021 at 09:18:24AM -0600, Adam Ford wrote:
> On Wed, Nov 24, 2021 at 11:42 PM Jagan Teki wrote:
> > On Tue, Nov 23, 2021 at 7:29 PM Adam Ford wrote:
> > > On Sun, Nov 21, 2021 at 4:25 PM Laurent Pinchart wrote:
> > > > On Sat, Nov 06, 2021 at 10:54:23AM -0500, Adam Ford wrote:
> > > > > Most of the blk-ctrl reset bits are found in one register, however
> > > > > there are two bits in offset 8 for pulling the MIPI DPHY out of reset
> > > > > and these need to be set when IMX8MM_DISPBLK_PD_MIPI_CSI is brought
> > > > > out of reset or the MIPI_CSI hangs.
> > > > >
> > > > > Fixes: 926e57c065df ("soc: imx: imx8m-blk-ctrl: add DISP blk-ctrl")
> > > > > Signed-off-by: Adam Ford <aford173@...il.com>
> > > > > ---
> > > > >
> > > > > V2:  Make a note that the extra register is only for Mini/Nano DISPLAY_BLK_CTRL
> > > > >      Rename the new register to mipi_phy_rst_mask
> > > > >      Encapsulate the edits to this register with an if-statement
> > > > >
> > > > >  drivers/soc/imx/imx8m-blk-ctrl.c | 18 ++++++++++++++++++
> > > > >  1 file changed, 18 insertions(+)
> > > > >
> > > > > diff --git a/drivers/soc/imx/imx8m-blk-ctrl.c b/drivers/soc/imx/imx8m-blk-ctrl.c
> > > > > index 519b3651d1d9..581eb4bc7f7d 100644
> > > > > --- a/drivers/soc/imx/imx8m-blk-ctrl.c
> > > > > +++ b/drivers/soc/imx/imx8m-blk-ctrl.c
> > > > > @@ -17,6 +17,7 @@
> > > > >
> > > > >  #define BLK_SFT_RSTN 0x0
> > > > >  #define BLK_CLK_EN   0x4
> > > > > +#define BLK_MIPI_RESET_DIV   0x8 /* Mini/Nano DISPLAY_BLK_CTRL only */
> > > > >
> > > > >  struct imx8m_blk_ctrl_domain;
> > > > >
> > > > > @@ -36,6 +37,15 @@ struct imx8m_blk_ctrl_domain_data {
> > > > >       const char *gpc_name;
> > > > >       u32 rst_mask;
> > > > >       u32 clk_mask;
> > > > > +
> > > > > +     /*
> > > > > +      * i.MX8M Mini and Nano have a third DISPLAY_BLK_CTRL register
> > > > > +      * which is used to control the reset for the MIPI Phy.
> > > > > +      * Since it's only present in certain circumstances,
> > > > > +      * an if-statement should be used before setting and clearing this
> > > > > +      * register.
> > > > > +      */
> > > > > +     u32 mipi_phy_rst_mask;
> > > > >  };
> > > > >
> > > > >  #define DOMAIN_MAX_CLKS 3
> > > > > @@ -78,6 +88,8 @@ static int imx8m_blk_ctrl_power_on(struct generic_pm_domain *genpd)
> > > > >
> > > > >       /* put devices into reset */
> > > > >       regmap_clear_bits(bc->regmap, BLK_SFT_RSTN, data->rst_mask);
> > > > > +     if (data->mipi_phy_rst_mask)
> > > > > +             regmap_clear_bits(bc->regmap, BLK_MIPI_RESET_DIV, data->mipi_phy_rst_mask);
> > > > >
> > > > >       /* enable upstream and blk-ctrl clocks to allow reset to propagate */
> > > > >       ret = clk_bulk_prepare_enable(data->num_clks, domain->clks);
> > > > > @@ -99,6 +111,8 @@ static int imx8m_blk_ctrl_power_on(struct generic_pm_domain *genpd)
> > > > >
> > > > >       /* release reset */
> > > > >       regmap_set_bits(bc->regmap, BLK_SFT_RSTN, data->rst_mask);
> > > > > +     if (data->mipi_phy_rst_mask)
> > > > > +             regmap_set_bits(bc->regmap, BLK_MIPI_RESET_DIV, data->mipi_phy_rst_mask);
> > > > >
> > > > >       /* disable upstream clocks */
> > > > >       clk_bulk_disable_unprepare(data->num_clks, domain->clks);
> > > > > @@ -120,6 +134,9 @@ static int imx8m_blk_ctrl_power_off(struct generic_pm_domain *genpd)
> > > > >       struct imx8m_blk_ctrl *bc = domain->bc;
> > > > >
> > > > >       /* put devices into reset and disable clocks */
> > > > > +     if (data->mipi_phy_rst_mask)
> > > > > +             regmap_clear_bits(bc->regmap, BLK_MIPI_RESET_DIV, data->mipi_phy_rst_mask);
> > > > > +
> > > >
> > > > Is it the best option to enable/disable both the master and slave MIPI
> > > > DPHY, regardless of whether they're used or not ? Or would it be better
> > > > to implement a reset controller to expose the two resets independently,
> > > > and acquire them from the corresponding display and camera drivers ?
> > >
> > > In some early attempts to implement the blk-ctrl driver, there was an
> > > attempt to enable a reset controller, but it caused some hanging and
> > > issues with suspend-resume due to chicken-egg issues where some items
> > > were coming up in the wrong order.  I think the decision was made to
> > > make the resets part of the power domain so it's very clear that the
> > > order of operations.  Lucas might be able to elaborate more on this.
> >
> > I think supporting via phy driver make sense to me since this resent
> > is DPHY specific and nothing related to blk-ctrl.
> 
> I would disagree that isn't not blk-ctrl.  The blk-ctrl controls the
> reset lines for the CSI and enables clocks.  The additional register
> does the same thing to the MIPI CSI and DSI.  The imx7-mipi-csis
> driver configures the dphy already, but this reset bit is not part of
> its IP block.  It seems weird to me that a phy driver would reference
> a phy driver.
> 
> > > If bits 16 and 17 can act independently and bit 16 only impacts the
> > > CSI  and doesn't require bit 17, it seems reasonable to me to have the
> > > power-domain part of  the CSI, since this would only be enabled when
> > > the CSI is active.  The power domain is idled when the CSI is idled
> > > which would effectively place the phy in and out of reset only
> > > depending on the state of the CSI.  I am guessing this reset bit
> > > should be assigned to DISPBLK_PD_MIPI_CSI and not
> > > DISPBLK_PD_CSI_BRIDGE, but I can run some more tests.
> > >
> > > AFAIK, there is no phy driver for the CSI like there is the DSI, so
> > > adding that would require additional work to the CSI driver to work
> > > around this quirk.  We don't have an acceptable DSI driver yet, so I'd
> > > like to push a V3 with just the corresponding bit enabled for MIPI_CSI
> > > after some testing.  FWICT, NXP set both bits 16 and 17 in their ATF
> > > gpc code, and it never gets cleared, so I think having the bit set and
> > > cleared on demand is an improvement.
> >
> > How about using the previous one that Marek sent. Add it via CSI
> > pipeline and i think it would directly.
> 
> That driver specifically addresses the DSI phy and bringing it out of
> reset is just one small part of what that driver does.  I don't think
> adding CSI functionality to it would be appropriate for that driver as
> they are separate IP blocks.
> 
> If people don't want the blk-ctl to control this bit, I would advocate
> we should do a separate reset controller to be referenced byt the
> mipi-csis driver, but that was proposed before and declined.  Since
> blt-ctrl already is pulling seemingly unrelated IP blocks by
> controlling their clocks and resets.  The fact that NXP included it in
> their ATF power-domain controller tells me they considered it related
> to power domains and/or resets and not an explicit phy driver.

I think it's a bit more complicated than that, unfortunately. The
BLK_CTRL is a mix of miscellaneous configuration bits thrown together.
It contains enable/disable bits for clocks and resets, but also D-PHY
configuration parameters (GPR_MIPI_[MS]_DPDN_SWAP_{CLK,DAT} in
GPR_MIPI_RESET_DIV, and all the fields of the GPR_MIPI_M_PLL* and
GPR_MIPI_[BMS]_DPHYCTL* registers). The latter should be controlled by
PHY drivers, but we may be able to control get away with hardcoded
values (possibly even hardware reset default values).

For the resets and clocks, reset and clock controllers could have been
nice. I'm not sure if controlling them through a power domain could
count as a bit of an abuse, as the power domain doesn't control power
rails, but looking at the imx8m-blk-ctrl driver the on/off sequences
required by the clocks and resets would be difficult to handle if clocks
and resets were exposed separately. I'd say that in the worst case it's
probably an acceptable hack.

For the D-PHY resets, exposing them through a reset controller would
also be (in my opinion) the most pedantic approach, bus as we have power
domains for the CSI and DSI controllers, controlling the corresponding
D-PHY resets from there is in no case worse that what we have already.

The only part that bothers me is the control of the master D-PHY, used
for MIPI DSI, from the MIPI CSI power domain. I've received feedback
from NXP today that those two GPR reset signals are connected directly
to the corresponding D-PHY, without any special combinatorial logic
in-between. I think it would be worth a try to control bit 16 from the
MIPI CSI power domain and bit 17 from the MIPI DSI power domain,
especially given that bit 17 didn't make any difference in my camera
tests on the i.MX8MM (I couldn't test display as my board doesn't use
the DSI output). If we then run into any issue, we can try to figure it
out.

> > https://www.spinics.net/lists/devicetree/msg381691.html

-- 
Regards,

Laurent Pinchart

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